Stack injection molding melt transfer system

ABSTRACT

This invention relates to injection molding and particularly to a melt transfer system for stack molding. According to the invention, a novel combination of known melt flow control valve units are arranged and operated to control the flow of pressurized melt from the stationary platen adjacent the molding machine to a manifold in the center moving platen. One control valve unit is located in the stationary platen in alignment with another control valve unit located in the moving platen. When the moving platen is in the closed position adjacent the stationary platen, the gates of the two control valve units abut and when the valve pins of the two control valve units are actuated to the open position, pressurized melt will flow through the gates from the stationary platen to the moving platen. The hot runner passage extends from the molding machine through the control valve unit located in the stationary platen. Through the gates into the control valve unit located in the moving platen, and then through the manifold system to the cavities located on opposing faces of the moving platen. In a second embodiment, a first cavity is located between the above two gates, and a third control valve unit is located in the moving platen in abutting alignment with the second control valve unit and its gate extends to a second cavity of the opposite face of the moving platen.

This is a division of application Ser. No. 970,388 filed Dec. 18, 1978.

BACKGROUND OF THE INVENTION

This invention relates generally to injection molding and, moreparticularly, to a new valve gated melt transfer system for stackmolding.

Stack molding provides the advantage that it enables the machine outputto be doubled without increasing its size. The location of the cavitieson opposing faces of the moving center section or platen makes thispossible because the same machine forces are applied to two cavities inseries rather than to a single cavity or parting line. However, stackmolding has the disadvantage that the melt runner system must extendthrough the moving center platen to reach the cavities.

In the past, the melt has been conveyed across the first parting linebetween the stationary platen adjacent the molding machine and themoving platen by a heated sprue tube or bar through the stationaryplaten from the machine nozzle across to the moving center platen. Thisstructure has the disadvantages that the heated tube is is the way whenthe mold is open and damages falling parts. Insulating it takes spaceand thereby reduces the number of cavities possible on the first partingline. Furthermore, when the heated tube loses contact with the machinenozzle, melt drools out and provides undesirable air entry into thesystem. In addition, the melt conveying passage is longer because it hasto cross the opening when the mold is open, thus resulting in higherpressure drop.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to at leastpartially overcome these disadvantages by providing an improved stackmolding melt transfer system using a combination of known valve gateunits to control the flow of melt to the center moving platen.

To this end, in one of its aspects, the invention provides stackinjection molding apparatus for conducting pressurized melt to amoveable platen which is actuated between an open and a closed positioncomprising a first melt flow control valve unit securely located in astationary platen, said first flow control valve unit having a moldingmachine inlet and a first controlled gate, said molding machine inletand said first controlled gate being connected by a first runnerpassage, and a second melt flow control valve unit securely located inthe moveable platen, said second flow control valve unit having a secondcontrolled gate and a second runner passage extending from said secondcontrolled gate, said second flow control valve unit being located insaid moveable platen in a position wherein said first and secondcontrolled gates are in conducting communication when the moveableplaten is in the closed position, said flow control valve units beingactuated to open and then close both of said gates while the moveableplaten is in the closed position to provide a flow of pressurized meltfrom the first runner passage to the second runner passage.

In another of its aspects, the invention further provides a method ofstack injection molding using a mold having a plurality of cavitieslocated on first and second parting lines, the first parting lineextending between a stationary platen and a first moveable platen, thesecond parting line extending between said first moveable platen and asecond moveable platen, the stationary platen having a first flowcontrol valve unit which has a first runner passage extending from amolding machine inlet to a first controlled gate, the first moveableplaten having a second flow control valve unit which has a second runnerpassage extending from a second controlled gate to communicate with saidcavities, comprising the steps of repeatedly closing the mold along saidfirst and second parting lines to form said cavities, said first andsecond controlled gates being in an abutting aligned relationship inthis closed position, actuating said first and second flow control valveunits to open said first and second controlled gates to provide for theflow of pressurized melt from the molding machine through said firstrunner passage through said open gates and through said second runnerpassage into said cavities, actuating said first and second flow controlvalve units to close said first and second controlled gates, and thenopening the mold along said first and second parting lines to eject themolded parts after the melt has set.

Further objects and advantages of the invention will appear from thefollowing description taken together with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of a known melt flow control valveunit;

FIG. 2 is a sectional view illustrating apparatus according to a firstembodiment of the invention, shown in the closed position;

FIG. 3 is a sectional view illustrating apparatus according to a secondembodiment of the invention, shown in the closed position; and

FIG. 4 is a sectional view illustrating the apparatus according to thesecond embodiment of the invention, shown in the open position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first made to FIG. 1 which shows a known melt flow controlvalve unit 10 positioned and screw mounted between a molding machine 12and a cavity 14. A hot runner passage 16 extends from the nozzle 17 ofthe machine 12 through the back plate 18, through bushing seal 20, pastthe stem 22 of the valve pin 24, through the gate 26 and into the cavity14. The heater cast 28 formed of beryllium copper has a electricalheating element 30 and a nozzle portion 32. The valve pin 24 is actuatedto its closed position with its tip 25 seated in the gate 26 by therocker arm 34 which is pivoted on rounded pin 36 seated in the backplate 18 by piston 38 which reciprocates in pneumatic cylinder 40. Theheater cast 28 is held in position by insulation bushing 42 and spacedfrom the cavity plate 44 by air gap 46. A nozzle seal 48 extends acrossthe air gap 46 adjacent the gate 26.

Referring now to FIG. 2, it illustrates a stack molding system using acombination of melt flow control valve units according to a firstembodiment of the invention. Each control valve unit is of the knowntype described above in regard to FIG. 1 and therefore the samereference numerals will be used in referring to their components, whenapplicable. As may be seen a first melt flow control valve unit 50 islocated in the stationary platen 52 adjacent the molding machine 12 anda second melt flow control valve unit 54 is located in the centralmoving platen 56. The moving platen 56 has a manifold system 58 whichextends to a plurality of cavities 60 located on opposing parting faces62, 64 of the moving platen 56. Both control valve units are the sameexcept that in the second 54, the back plate is replaced by a portion ofthe manifold plate 65. The moving platen 56 is reciprocated between anopen position and the closed position shown, in which one parting face62 of the moving platen 56 meets the stationary platen 52 along a firstparting line 66 while the other parting face 64 meets a second movingplaten (not shown) along a second parting line 68. The first and secondmelt flow control valve units 50, 54 are located in the stationaryplaten 52 and moving platen 56 respectively so that their gates are inabutting alignment in this closed position.

In use, the central moving platen 56 is actuated away from thestationary platen 52 to the open position to eject the previously formedproduct and then returned to the closed position. The hot runner passage70 extends from the molding machine nozzle 17, through the first meltflow control valve unit 50, through the second melt flow control valveunit 54, through the manifold system 58 in the moving platen 56 and is,in this embodiment edge gated into the cavities 60. The rocker arms 34of both control valve units 50, 54 are pneumatically actuated by thepistons 38 to their open positions which releases the pressure on thevalve pin allowing the pressurized melt to open them and flow past thetip of the valve pin and out the gate of the first control valve unit 50and into the abutting gate of the second control valve unit 54. Afterthe cavities 60 are filled, the pistons 38 of the respective controlvalve units are actuated to force the valve pins 24 to their closedpositions seated in their respective gates with their tips 25 abuttingon the first parting line 66. After a period of time has passedsufficient to allow the molded parts to set, the moving platen 56 isactuated to the open position to eject the parts and the closed controlvalve units prevent leakage or drooling of the melt. The moving platen56 is then returned to the closed position and the pressure to thepistons 38 is relieved to allow the valve pins to return to their openpositions under the melt pressure to all the melt to flow through therunner passage 70 to the cavities 60. This process may be repeated atspeeds up to about twenty times per minute and a large number ofcavities may be fed from the manifold system 58 in the moving platen 56.

FIGS. 3 and 4 illustrate another stack molding system using apparatusaccording to a second embodiment of the invention. In this embodiment,the components of the melt flow control valve units are again similar tothose described in regard to FIG. 1 and therefore, the same referencenumerals will again be used in referring to them, when appropriate. Inthis system, there is a stationary platen 52, a first moving platen 56and a second moving platen 72 which is shown in FIG. 4, and the firstcontrol valve unit 50 is again located in the stationary platen 52. Thesecond control valve unit 54 is also located in the moving platen 56,but in addition, a third melt flow control valve unit 74 is located inthe first moving platen 56 in abutting, but opposed relationship to thesecond control valve unit 54. Furthermore, while the gates 26 of thefirst and second control valve units 50, 54 are in alignment when themoving platens are in the closed position, the gates are spaced across afirst cavity 76 located along the first parting line 66 between thestationary platen 52 and the first moving platen 56. The third melt flowcontrol valve unit 74 is located with its gate extending to a secondcavity 78 located on the second parting line 68 between the first andsecond moving platens 56, 72 and the other end of the third controlvalve unit 74 abuts on the second control valve unit at locating andsealing ring 80. The hot runner passage 70 extends from the nozzle 17 ofthe molding machine 12 through the first control valve unit 50, acrossthe first cavity 76, through the second and third control valve units54, 74 and into the second cavity 78.

In use, with the moving platens in the closed position shown in FIG. 3,the air pressure to the pistons 38 of all three control valve units isreleased to allow the valve pins to move to their open positions underthe pressure of the melt. The melt then flows through the hot runnerpassage 70 and fills the first and second cavities 76, 78. After thecavities are filled the pistons 38 of all the control valve units areactuated to return the valve pins 24 to their closed positions withtheir tips seated in their respective gates. After the parts have set,the moving platens are opened to eject the parts and then returned totheir closed positions, and the process is repeated.

Although this invention has been described in respect to two particularembodiments, it is not to be construed in a limiting sense. Manyvariations and modifications will now occur to those skilled in the art.In particular, it will be apparent that the invention is not limited tothe use of these particular control valve units.

What I claim is:
 1. A method of stack injection molding using a moldhaving a plurality of cavities located on first and second partinglines, the first parting line extending between a stationary platen anda first moveable platen, the second parting line extending between saidfirst moveable platen and a second moveable platen, the stationaryplaten having a first flow control valve unit which has a first runnerpassage extending from a molding machine inlet to a first controlledgate, the first moveable platen having a second flow control valve unitwhich has a second runner passage extending from a second controlledgate to communicate with said cavities, comprising the steps ofrepeatedly:(a) closing the mold along said first and second partinglines to form said cavities, said first and second controlled gatesbeing in an abutting aligned relationship in this closed position; (b)actuating said first and second flow control valve units to open saidfirst and second controlled gates to provide for the flow of pressurizedmelt from the molding machine through said first runner passage, throughsaid open gates and through said second runner passage into saidcavities; (c) actuating said first and second flow control valve unitsto close said first and second controlled gates, and then (d) openingthe mold along said first and second parting lines to eject the moldedparts after the melt has set.